fdo#86131 SwXTextField::getAnchor: handle postit field with annotation mark

(cherry picked from commit 2608512056b706bab57e36765e15f5c00668577a)

Conflicts:
	sw/qa/extras/uiwriter/uiwriter.cxx

Change-Id: I3881c4577375a2eda053f64800d0991de6f009ad
Reviewed-on: https://gerrit.libreoffice.org/12979
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>